The evolution of radio access schemes and wireless networks for cellular mobile communication (hereinafter referred to as “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access: EUTRA”) has been studied by the 3rd Generation Partnership Project (3GPP). In LTE, an orthogonal frequency division multiplexing (OFDM) scheme has been used as a communication scheme in the downlink from a base station apparatus to a mobile station apparatus. In addition, an SC-FDMA (Single-Carrier Frequency Division Multiple Access) scheme has been used as a communication scheme in the uplink from a mobile station apparatus to a base station apparatus. Here, in LTE, a base station apparatus is also called an eNodeB (evolved NodeB) and a mobile station apparatus is also called a UE (User Equipment). LTE is a cellular communication system in which a plurality of areas covered by a base station apparatus are arranged in a cellular form.
In LTE, a base station apparatus instructs a mobile station apparatus to perform initial transmission or retransmission of a PUSCH (Physical Uplink Shared Channel), which is a channel used for transmission of uplink data (or also referred to as an “uplink shared channel: UL-SCH”), by using Downlink Control Information (DCI) that is transmitted on a PDCCH (Physical Downlink Control Channel). A mobile station apparatus transmits a PUSCH in accordance with received downlink control information to a base station apparatus. A mobile station apparatus transmits a DMRS (Demodulation Reference Signal) together with a PUSCH to a base station apparatus. A DMRS is used in a base station apparatus for channel estimation and the like.
In LTE Release 11, support of Coordinated Multipoint Transmission/Reception (CoMP) in which interference coordination is performed between base station apparatuses (cells or transmission/reception points) in a mutually coordinated manner has been studied as a method of reducing or preventing interference with a mobile station apparatus or a base station apparatus. A transmission/reception point represents a transmission point and a reception point of a signal. A transmission/reception point may be a base station apparatus, for example (NPL 1).
In the case where a plurality of mobile station apparatuses that communicate with different cells (base station apparatuses or transmission/reception points) transmit PUSCHs in partially overlapping frequency bands, interference with an adjacent cell becomes a problem. FIG. 11 is a diagram illustrating interference signals from mobile station apparatuses to adjacent cells in the related art. In FIG. 11, an area covered by a base station apparatus A (transmission/reception point A) is a cell A, and an area covered by a base station apparatus B (transmission/reception point B) is a cell B. A mobile station apparatus A transmits a PUSCH and a DMRS to the base station apparatus A (transmission/reception point A), and a mobile station apparatus B transmits a PUSCH and a DMRS to the base station apparatus B (transmission/reception point B). In FIG. 11, thick arrows represent desired signals and dotted arrows represent interference signals.
In FIG. 11, in the case where a frequency band scheduled by the base station apparatus A for a PUSCH from the mobile station apparatus A partially overlaps a frequency band scheduled by the base station apparatus B for a PUSCH from the mobile station apparatus B, a PUSCH and a DMRS transmitted by the mobile station apparatus A become interference signals that interfere with the base station apparatus B, and a PUSCH and a DMRS transmitted by the mobile station apparatus B become interference signals that interfere with the base station apparatus A. To solve the foregoing problem, NPL 1 describes a technique in which, in the case where a plurality of mobile station apparatuses transmit PUSCHs in partially overlapping frequency bands, different base sequences for DMRSs are assigned to the mobile station apparatuses respectively.